The fundamental aspects of the control of follicular development in monotocous species will be examined using the rhesus monkeys as an experimental model. First, using a dual label autoradiographical procedure, the kinetics of follicular growth at defined stages of the menstrual cycles will be analyzed. The results of these experiments will provide information regarding the development of preantral and early antral follicles and the fate of growing follicles during the early follicular, late follicular and luteal phase of the menstrual cycle. Additional experiments will be performed to determine the length of time required for a follicle to develop to a fully mature Graafian follicle. Second, the responsiveness of follicles to exogenous gonadotropins at defined stages of the menstrual cycle will be investigated to determine if follicles are refractory or have a diminished sensitivity to hormonal stimulation at stages of the menstrual cycle characterized by an absence of secondary follicular development. Correlated with the experiments will be an analysis of the number of follicles which have gonadotropin binding sites in either thecal or granulosa. These experiments will provide information regarding the mechanism by which secondary follicle development is arrested during the late follicular and luteal phase of the cycle. Third, experiments will be performed to determine if estradiol acts locally in the ovaries to enhance preantral follicular development. For this purpose a repository source of estradiol will be placed into ovaries of hypophysectomized monkeys and the morphology of the ovaries containing estradiol and the sensitivity of these ovaries to exogenous gonadotropin will be determined and compared with the ovaries not containing estradiol.